1. Field of the Invention
The invention pertains to an apparatus and a method for carrying out a vibroacoustic inspection of a motor vehicle that features at least a front and a rear axle, with a test stand that is directly or indirectly connected to at least one of the two axles by means of a force flow and relative to which the motor vehicle is tied, wherein at least one vibration generator of a first type is provided along the force flow in order to generate vibrations below 50 Hz. The invention furthermore pertains to a method for vibroacoustic inspection of motor vehicles.
2. Description of the Prior Art
Test stands on which a motor vehicle is to be inspected, that are driven on rollers or rolls in a self-propelled fashion, are used for experimentally determining the vibroacoustic behavior of motor vehicles in the laboratory. FIG. 2 schematically shows a known roller-type test stand, in which at least the wheels of the vehicle 1 that are driven by the driving axle are in rolling contact with rollers 2 of the roller-type test stand. A heavy-duty electric motor 3 serves for driving and decelerating (absorbing the load of) the rollers 2, wherein the operating mode of the electric motor is controlled by a control and monitoring unit 4. An at least soundproof (semi-anechoic) measuring chamber, that surrounds the entire test stand, is required for carrying out a vibroacoustic inspection of the motor vehicle situated on the rollers 2 in order to obtain information on driving noises inside and outside the motor vehicle 1 under defined ambient conditions. According to the schematic representation shown in FIG. 2, roller-type test stands of this type are technically complex and therefore very costly, wherein these test stands also require much space. Known roller-type test stands also do not make it possible to realistically simulate the vibroacoustic behavior of a vehicle while driving maneuvers are executed. Another decisive disadvantage is the low flexibility with respect to the driving surfaces that can be simulated, particularly in light of the fact that a change of the road surface requires costly and time-consuming adaptations of the driving rollers and the driven rollers, respectively.
Various concepts that make it possible to subject a vehicle to different loads in the vertical direction of the vehicle, for example, as illustrated in the test stand according to FIG. 3, have been proposed in order to solve the problem of simulating driving maneuvers and different operational loads on a test stand. In this case, the motor vehicle 1 is situated on lifting platform elements that can be vertically raised in a servohydraulic fashion, wherein the two front lifting platform elements of the embodiment shown are equipped with motor-driven continuous bands 2, on which the front wheels driven by the vehicle are positioned. Corresponding electric motors 3 are provided for driving the two separate running bands 2. Although test stands of this type make it possible to introduce specific loads into the motor vehicle 1 along the vertical direction of the vehicle, the problem of a flexible change of the road surface also remains unsolved in this case.
There is an urgent need for an experimental simulation environment that is able to simulate operational loads as well as driving maneuvers and highly dynamic loads as realistically as possible under laboratory conditions, wherein this need is justified by advancing developments in the field of active and, in particular, adaptive chassis components that not only serve for optimizing the driving characteristics with respect to an improved roadability, but also for reducing sounds and vibrations occurring within the motor vehicle and therefore contribute to improving the safety and the comfort. The stimulation of high-frequency vibrations emanating from the vehicle is primarily caused by the rolling contact between the tires and the road surface and is significantly influenced by the tire profile and the road surface quality, wherein these high-frequency vibrations contribute to the overall acoustic properties of the motor vehicle and therefore need to be individually determined and correspondingly analyzed. Although conventional test stands with servohydraulic load application units as, for example, in accordance with the embodiment shown in FIG. 3, make it possible to experimentally simulate nearly all degrees of freedom acting upon the vehicle. Test stands of this type reach their technical limits with respect to the frequency range of the vibrations introduced into the vehicle at approximately 50 Hz.